It has therefore been suggested that the valves of a hydraulic transmission such as utilized in vehicles can be controlled by a microprocessor which includes sensors that sense variables such as road speed, throttle position and engine rpm and functions to provide pulses to pulse width modulated valves which in turn control spool valves operating clutches in the transmission or control clutches directly.
In such pulse width modulator valves, it is desirable to be able to accurately control the pressure of the fluid.
The space requirements are quite small and therefore require a small valve which will function effectively in a pulse modulated mode to provide the fluid at constant pressure.
Accordingly, among the objectives of the present invention are to provide a solenoid valve which is small, utilizes a minimum number of parts to produce the desired control of pressure and can be used in a pulse width modulated mode or a steady state directional mode.
In accordance with the invention, the solenoid valve comprises a housing including a transverse wall, an integral axial extension extending from the transverse wall, and an integral peripheral wall extending axially in the opposite direction from the periphery of the transverse wall. The solenoid valve includes a center pole member which includes a pole extending axially within the peripheral wall of the housing. The center pole includes an integral transverse wall extending radially outwardly into engagement with the peripheral wall of the housing. The center pole includes an integral axial extension extending in the opposite direction from said axial extension of the housing. The housing and the transverse wall of the pole member support a coil which surrounds the pole pieces. The axial extension of the housing includes an axial opening and the center pole includes an axial opening aligned with the opening of the the axial extension. The end of the center pole within said housing defines a first valve seat and the axial extension of the housing defining a second valve seat. A ball has limited axial movement between the seats. The major portion of the ball extends into a cavity adjacent the second seat in the axial extension. The coil is spaced from the periphery of the center pole. A groove is formed in the center pole at the area of juncture of the center pole and transverse wall on the center pole member and a plurality of circumferentially spaced axially extending passages extend from the groove to the periphery of the center pole member such that when fluid is applied through the axial opening of the center pole member, it forces the ball against the second seat on the axial extension and fluid flows about the pole piece to the annular groove and thereafter outwardly through the axial passages and when the coil is energized, the ball is drawn toward the pole piece to seal against the first seat and communication is provided between the axial opening of said axial extension and the axial passages about the ball and the periphery of the pole piece.